1. Field of the Invention
Aspects of the present invention relate to a cognitive radio (CR) environment, and more particularly, to a method and apparatus for controlling a transmission power of a CR environment.
2. Description of the Related Art
Due to the rapid development of wireless communication technologies, wireless communication systems are currently required to obtain and maintain their own frequency band to overcome disadvantages resulting from the coexistence of a plurality of systems. However, frequency resources for new wireless communication systems are virtually exhausted since most frequency bands that are actually available are already assigned according to government policy. That is, according to current frequency assignments, frequency bands from Hz to GHz are all being used, leaving no frequency bands that may additionally be used.
Cognitive radio (CR) technology is currently being discussed to overcome such radio resource shortages. In CR technology, radio resources with a low utilization ratio are identified and then shared without interfering with systems that use existing assigned frequencies. Accordingly, radio resource efficiencies are theoretically improved.
Cost efficiency is one of the advantages of CR technologies. Specifically, compared to existing wireless communication services, CR technologies are relatively low priced by using wireless frequency bands with no charge. CR technologies are related to the management and distribution of wireless channels with respect to multi-channels and to interference detection technologies, which may be interoperable with next generation wireless communication. As an example, CR technologies may efficiently transmit high speed data in dead zones without generating frequency interferences. In this instance, the dead zones are created in cellular environments or rural areas required to improve cell sizes.
FIG. 1 is a diagram illustrating an example of a conventional CR environment. Referring to FIG. 1, a signal process operation in an existing CR environment 100 where an incumbent user 152 exists is described. An incumbent user 152 is a priority and/or previous user of a frequency utilized in the existing CR environment 100.
As illustrated in FIG. 1, a single CR base station 101 and a plurality of CR users 102, 103, 104, 105, 106, 107, 108, 109, and 110, which communicate using a CR technology, control a communication to be performed by using given radio frequency resources (e.g. channel 1, channel 2, channel 3, etc.). Accordingly, the CR base station 101 divides and manages a wireless communication network. The CR users 102, 103, 104, 105, 106, 107, 108, 109, and 110 are referred to as customer premises equipment (CPE). Two of the CR users 102 and 103 that use the channel 1 may use channel 1 in a same frequency band by separating channel 1 in terms of time based on an orthogonal frequency division multiple access (OFDMA). In this case, when an incumbent user 152 that uses channel 1 in the same frequency band exists around the CR user 102 in the communication area of the CR environment 100 and communicates with an incumbent base station 151, the CR user 102 is required to not interfere with the incumbent user 152. Accordingly, the CR user 102 is required to vacate a frequency band of channel 1 that is being used.
FIG. 2 is a diagram illustrating an example of an environment of a general wireless communication system. Referring to FIG. 2, a case where a wireless communication user that uses a same frequency band in an environment of at least two conventional wireless communication systems exists is described. It is understood that a wireless communication system described in FIG. 2 may be, for example, a communication system of a CR environment.
As illustrated in FIG. 2, the at least two wireless communication systems using the same frequency band may exist. Two wireless communication base stations 201 and 251 exist and control communication areas 200 and 250, respectively. A signal transmitted by the wireless communication base station 201 or 251 is received by the wireless communication user. A maximum distance that is decodable at all times is a protected zone 204. An interference power, which is predictable or unpredictable, may be received in the environment of the wireless communication system. Accordingly, considering a zone 205 for a particular signal-to-noise ratio, a decodable zone 203 with respect to a signal received from a wireless communication base station may be divided. That is, when the wireless communication user is located in the protected zone 204, the signal received from the wireless communication base station 201 may be decodable at all times. However, when the wireless communication user is located in the decodable zone 203, the signal received from the wireless communication base station 201 may or may not be decodable due to an effect of interference.
In the wireless communication system environments, when a same radio resource (i.e., another wireless communication user communicating with the wireless communication base station that uses a same frequency band) exists, a common communication area 210 is generated. The common communication area 210 is between areas controlled by the two wireless communication base stations 201 and 251. In this instance, a co-channel interference or radio interference may occur in two wireless communication users 202 and 252, while receiving a signal received from the two wireless communication base stations 201 and 251.
A communication method and apparatus of a conventional CR environment has the following disadvantages. First, in the conventional CR environment, when an incumbent user exists, CR users that do not cause a channel interference may not use a channel that the incumbent user uses. For example, as illustrated in FIG. 1, when the incumbent user 152 exists, the two CR users 103 and 104 may not use the channel 1 even though the two CR users 103 and 104 do not interfere with the incumbent user 152. Second, in the conventional CR environment, a channel change frequently occurs due to the existence of an incumbent user, which causes a communication time delay and a system instability.
Accordingly, a method and apparatus for controlling a transmission power of a CR environment is needed.